We all know that China has been banning giant apps like Facebook even before. So if China does it, the US can also do what they want especially if they are seeing that TikTok is a threat to their people. But if they keep on doing such an act, it won't stop and might cause a bigger issue between the two.
I suppose President Trump has valid reasons to ban Tiktok and WeChat and I guess its more about national security its very obvious that China is exerting its influence over many aspects of society globally through these social media giants - and this is much like how China feels by banning Facebook and Google - which I think this is also a response in light with these previous incidents.
My only concern is that the U.S may find having a hard time banning these companies totally as we all know some people may find a way circumvent it not unless the U.S. lays down solid technical infrastructure to fully enforce this ban order.